Plating device

ABSTRACT

A plating device equipped with a plating tank and an impurity removal mechanism disposed so as to remove impurities from a plating solution in the plating tank or a plating solution to be supplied to the plating tank, in which the impurity removal mechanism includes at least one of a carboxylic acid removal mechanism and an alcohol removal mechanism.

TECHNICAL FIELD

The present invention relates to a plating device. More specifically, the present invention relates to a plating device for manufacturing an electrically conductive pattern used in various kinds of electronic parts, and particularly, it relates to a plating device for forming a planar coil by electroplating.

BACKGROUND

In recent years, the shape of the planar coil parts used in electronic equipment is also required to be miniaturized, thinned, lightened in association with miniaturization, thinning, and weight saving of the electronic equipment, and the improvement in coil performance in the volume thereof is strongly desired from the standpoint of product performance. As a representative manufacturing method of a coil, a manufacturing method by etching and plating is mentioned. In recent years, however, a manufacturing method by a plating process is indispensable since a coil which has a narrow space between the lines, a small gap, and thus has a high space factor is demanded. As the plating process, a semi-additive manufacturing method to be described later is well known.

In the semi-additive method, a resist is formed on the surface of an underlying conductor layer that has been previously formed on an insulating substrate so as to cover it other than the coil portion, and electroplating by direct current is conducted by taking the underlying conductor layer as a base to form a conductor layer. Thereafter, the resist pattern is peeled off therefrom, and the unnecessary underlying conductor layer exposed by peeling off of the resist pattern is then removed by etching.

Copper sulfate plating is used in the formation of a general planar coil. A copper sulfate plating solution is a solution prepared by mixing and dissolving sulfuric acid and copper sulfate as main components in a solvent and adding an additive and chlorine to this.

A schematic diagram of a plating device of the prior art is illustrated in FIG. 4. As illustrated in FIG. 4, a plating device 1 of the prior art is equipped with a plating tank 2 for plating an object to be plated 10, a management tank 4 for storing a plating solution 3 overflowed from the plating tank 2, a plating solution transport system 5 for circulating and transporting the plating solution 3 from the management tank 4 to the plating tank 2, and an anode 9.

The plating solution transport system 5 is constituted by a pump 6 for transporting the plating solution 3, a flow valve 7 for adjusting flow rate of the plating solution 3, a filter 8 for removing impurities in the plating solution, and a flow meter 17 for measuring flow rate of the plating solution 3.

A structural example (cross-sectional diagram) of the object to be plated 10 is illustrated in FIG. 3. The object to be plated 10 is one that is obtained by forming an underlying conductor layer 12 on the surface of a substrate 11 and being patterned with a resist 13, and the object to be plated 10 has a contact portion 14 for applying a current to the underlying conductor layer 12.

Next, the operation of the plating device of the prior art will be described. First, the object to be plated 10 is immersed in the plating solution 3. It is possible to deposit a metal on the surface of the underlying conductor layer 12 by applying a current from the anode 9 to the underlying conductor layer 12. It is possible to apply a current to the underlying conductor layer 12 via the contact portion 14.

At this time, the metal constituting the anode releases an electron to be an ion on the anode surface, and the metal ion dissolves into the plating solution 3. The underlying conductor layer 12 is formed on the surface of the substrate 11, thus the metal ion in the plating solution 3 receives an electron on the surface thereof, and the metal is deposited on the surface of the underlying conductor layer 12. The plating solution 3 is supplied from a supply port 18 to the plating tank 2 and then overflows the plating tank 2.

In the plating device 1 of the prior art having the above constitution, the organic component contained in the resist 13 dissolves into the plating solution 3 even though it is a trace amount when the resist 13 is immersed in the plating solution 3. The plating solution 3 is repeatedly used by being circulated and transported between the plating tank 2 and the management tank 4, and when the plating device 1 of the prior art is used for a long period of time, the eluted substance of the resist increases in the plating solution 3 and thus causes a defect such as fogging or a protrusion on the plated film, which is a problem.

In order to solve this, generally the plating solution is regenerated by filtering the plating solution through an activated carbon filter to remove the eluted substance of the resist in the plating solution. However, it is difficult to selectively remove the eluted substance of the resist by filtration using an activated carbon filter.

In order to solve this, a method in which an organic solvent is added to the plating solution and the organic substance in the plating solution is extracted and removed with the organic solvent is proposed (Patent Literature 1).

CITATION LIST Patent Literature

[Patent Literature 1] Japanese Unexamined Patent Publication No. H4-272200

SUMMARY

However, the organic substance to cause a defect is not specifically identified in Patent Literature 1 described above, and the concentration of the organic substance (for example, additive) that is effective in the plating is also decreased by the extraction removal of the organic substance. As a result, there is a problem that the quality of the plated film is not stabilized by a change in concentration of the additive.

The present invention has been made to solve the above problem, and an object thereof is to provide a plating device which selectively removes an organic substance to cause a defect in the plating solution without decreasing the concentration of a useful additive and does not cause fogging or a protrusion on the plated film even when the plating device is used for a long period of time.

The present inventors have carried out intensive investigations to solve the above problem, and as a result, they have found out that the organic substance to cause a defect in the plating solution is the decomposition product of a solvent component (hereinafter, also referred to as a resist solvent component) contained in the resist, thereby achieving the present invention.

The decomposition product of the resist solvent component specifically refers to a decomposition product produced by hydrolysis of the ester bond of the organic solvent when the resist containing an organic solvent having an ester bond, for example, propylene glycol monomethyl ether acetate (PMA), ethyl lactate, or butyl acetate is immersed in an acidic plating solution. The decomposition product of an organic solvent is specifically a carboxylic acid and an alcohol.

The plating device of the present invention is equipped with a plating tank and an impurity removal mechanism disposed so as to remove impurities from a plating solution in the plating tank or a plating solution to be supplied to the plating tank, and the impurity removal mechanism includes at least one of a carboxylic acid removal mechanism and an alcohol removal mechanism. This makes it possible to suppress the generation of fogging or a protrusion on the plated film even when the plating device is used for a long period of time.

In addition, the device of the present invention is further equipped with a management tank for receiving the plating solution to be supplied from the plating tank and supplying the plating solution received to the plating tank again, and the carboxylic acid removal mechanism or the alcohol removal mechanism may be connected to the management tank.

This makes it possible to suppress a change in concentration of the plating solution in the plating tank and further to obtain a plated film having stable quality.

It is possible to selectively remove an organic substance to cause a defect in the plating solution without decreasing the concentration of a useful additive and to stably obtain a plated film without having fogging or a protrusion for a long period of time by using the plating device described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a plating device representing a first embodiment of the present invention.

FIG. 2 is a schematic diagram of a plating device representing a second embodiment of the present invention.

FIG. 3 is a cross-sectional diagram of an object to be plated.

FIG. 4 is a schematic diagram of a plating device of the prior art.

DETAILED DESCRIPTION First Embodiment

Hereinafter, a preferred mode for carrying out the present invention will be described. However, the technical idea of the present invention is not limited to the following embodiments.

A schematic diagram of a plating device 20 according to the first embodiment is illustrated in FIG. 1. The plating device 20 of the present embodiment is equipped with a plating tank 2 for plating an object to be plated 10, a management tank 4 for storing a plating solution 3 overflowed from the plating tank 2, a plating solution transport system 5 for circulating and transporting the plating solution 3 from the management tank 4 to the plating tank 2, an anode 9, and an impurity removal mechanism 19 that is connected to the plating tank and removes the impurities from the plating solution 3. The impurity removal mechanism 19 is divided into a carboxylic acid removal mechanism 15 and an alcohol removal mechanism 16.

The plating solution 3 can contain a component that is known in the prior art and used in electroplating, and it can contain a metal ion of a metal to be plated, an organic acid or an inorganic acid, and an additive. As the additive, those known in the prior art can be used, and examples thereof may include a plating inhibitor of a nonionic surfactant such as a chloride ion or polyethylene glycol, a sulfur-containing compound-based plating accelerator such as bis(3-sulfopropyl) disulfide, and a leveling agent such as Janus Green B. A metal ion of a metal to be plated is added to the plating solution in the form of a salt containing the metal ion, and examples thereof may include copper sulfate, copper chloride, and copper pyrophosphate in a case where the plating solution 3 is a copper plating solution. It is possible to use alkanesulfonic acid, sulfuric acid, or the like as the organic acid or the inorganic acid in a case where the plating solution 3 is a copper plating solution.

The resist formed on the object to be plated 10 contains the organic solvent having an ester bond described above. Examples of such an organic solvent having an ester bond may include propylene glycol monomethyl ether acetate (PMA), ethyl lactate, or butyl acetate. The carboxylic acid and the alcohol which are produced as the these organic solvent having an ester bond are hydrolyzed when being immersed in an acidic plating solution are to be a factor to cause fogging or a protrusion on the plated film when the plating device is used for a long period of time. Specific examples of such a carboxylic acid may include acetic acid and formic acid. Specific examples of such an alcohol may include 1-methoxy-2-propanol and 2-methoxy-2-propanol.

As the carboxylic acid removal mechanism 15, a mechanism which can selectively remove a carboxylic acid in the plating solution is used. Examples thereof may include an ion chromatography apparatus and a distillation apparatus. In particular, an ion chromatography apparatus which can selectively remove a carboxylic acid is preferable. It is possible to use a known arbitrary apparatus as the ion chromatography apparatus. Preferably, an apparatus that is referred to as a simulated moving bed is generally used. The distillation apparatus is not particularly limited as long as it can remove a carboxylic acid contained as impurities, and a distillation apparatus having a heating function to raise the temperature up to from 150 to 160° C. is preferable. The carboxylic acid removal mechanism 15 is preferably one that does not substantially remove the metal ion of the metal to be plated, the organic acid or the inorganic acid, and the additive described above from the plating solution 3, and it is preferable that a change in concentration of these components in the plating solution 3 which has passed through the carboxylic acid removal mechanism is 10% by mass or less as compared to the concentration of these components in the plating solution before passing through the carboxylic acid removal mechanism.

As the alcohol removal mechanism 16, a mechanism which can selectively remove an alcohol in the plating solution is used. Examples thereof may include a distillation apparatus and an activated carbon filter which can selectively remove an alcohol. Here, as the activated carbon, those obtained by supporting a metal catalyst such as platinum can be suitably used. As the distillation apparatus, particularly a distillation apparatus which can selectively remove an alcohol is preferable. As the distillation apparatus, a general distillation apparatus can be used, but a distillation apparatus having a heating function to raise the temperature up to from 150 to 160° C. is preferable. The alcohol removal mechanism 16 is preferably one that does not substantially remove the metal ion of the metal to be plated, the organic acid or the inorganic acid, and the additive described above from the plating solution 3, and it is preferable that a change in concentration of these components in the plating solution 3 which has passed through the alcohol removal mechanism 16 is 10% by mass or less as compared to the concentration of these components in the plating solution before passing through the alcohol removal mechanism 16.

Next, the plating operation by the plating device 20 illustrated in FIG. 1 will be described. First, the object to be plated 10 is immersed in the plating solution 3. The object to be plated 10 is the same as that illustrated in FIG. 3 described above. For the object to be plated 10, a metal can be deposited on the surface of the substrate 11 by applying a current from the anode 9 to the substrate 11. The plating solution 3 is supplied from the supply port 18 and overflows the plating tank 2.

A trace amount of the organic component eluted from the resist 13 of the object to be plated 10 is dissolved in the plating solution 3 overflowed. A defect such as fogging or a protrusion is caused on the plated film when this organic component is accumulated in the plating solution 3 and the amount thereof exceeds a predetermined amount.

Next, the regenerative action of the plating solution 3 by the plating device 20 illustrated in FIG. 1 will be described. First, the plating solution 3 containing the eluted substance of the resist is transported to the carboxylic acid removal mechanism 15 attached to the plating tank 2 by the pump 6. In a case in which the carboxylic acid removal mechanism 15 is an ion chromatography apparatus, a strongly acidic cation exchange resin is filled in the column of the ion chromatography apparatus, and the carboxylic acid in the plating solution 3 is adsorbed and removed as the plating solution 3 passes through the interior of the strongly acidic cation exchange resin. As the strongly acidic cation exchange resin, a gel-type sulfonic acid-type strongly acidic ion exchange resin in which a sulfonic acid group is bonded to a styrene-divinylbenzene copolymer is used.

Next, the plating solution from which the carboxylic acid has been removed is transported to the alcohol removal mechanism 16. In a case in which the alcohol removal mechanism 16 is a distillation apparatus, the temperature of the plating solution 3 is adjusted to be equal to or higher than the evaporating temperature of the alcohol by a heater in the distillation apparatus. Here, the alcohol in the plating solution 3 becomes a vapor, and the vapor is liquefied as it passes through the cooling tube, and removed. The plating solution 3 having a high temperature passes through the cooling tube that is adjusted to a predetermined temperature to return to the plating tank 2.

A defect such as fogging or a protrusion on the plated film is less likely to be caused even though a plating device having such a regeneration mechanism is used for a long period of time. This is because the impurity removal mechanism 19 selectively removes only the causative substance to cause a defect on the plated film.

Second Embodiment

FIG. 2 is a diagram illustrating the constitution of a plating device 21 according to the second embodiment. The impurity removal mechanism 19 is connected to the management tank 4 in FIG. 2. The constitution of the plating device 21 other than this is the same as the plating device 20 described in the first embodiment.

It is possible to more uniformly control a change in concentration of the plating solution 3 in the plating tank 2 by connecting the impurity removal mechanism 19 to the management tank 4. This makes it possible to have an effect of stabilizing the plated film to be obtained.

EXAMPLES

Hereinafter, the present invention will be further described with reference to Reference Examples and Examples.

(Function Confirmation of Impurity Removal Mechanism)

The effect of the impurity removal mechanism in a copper sulfate plating solution will be described with reference to Reference Examples 1 to 3. A copper sulfate plating solution was prepared so as to contain 200 g/L of copper sulfate pentahydrate, 100 g/L of sulfuric acid, and 50 mg/L of hydrochloric acid, and 100 mg/L of polyethylene glycol (PEG), 8 mg/L of bis(3-sulfopropyl)disulfide (SPS), and 10 mg/L of the Janus Green B (JGB) as the additive. Four sheets of a substrate in total obtained by coating a resist on a silicon wafer having a diameter of 6 inches so as to have a thickness of 30 μm were immersed in the copper sulfate plating solution and left to stand for 7 days to elute the impurities, thereby obtaining a sample solution. The impurities thus eluted were analyzed using an ion chromatography apparatus, IR, and NMR to confirm that the carboxylic acid was acetic acid and the alcohol was 1-methoxy-2-propanol.

Reference Example 1

The carboxylic acid in the sample solution was removed using an ion chromatography apparatus (trade name: DX-500 manufactured by Thermo Fisher Scientific K.K.), and the alcohol was removed by a distillation apparatus. The removal of the carboxylic acid by an ion chromatography apparatus was conducted using AS20 (column diameter: 4 mm) as the column under the condition having a flow rate of 1 ml/min. In addition, the removal of the alcohol by a distillation apparatus was conducted under the condition having a set heating temperature of 150° C. The removal of carboxylic acid and alcohol was conducted by allowing the entire sample solution to pass through the ion chromatography apparatus and the distillation apparatus one time.

Reference Example 2

The carboxylic acid and alcohol in the sample solution were removed by an activated carbon filter. The removal of carboxylic acid and alcohol was conducted by allowing the entire sample solution to pass through the activated carbon filter one time.

Reference Example 3

The carboxylic acid and alcohol in the sample solution were not removed.

The measurement results of the concentration of each component in the plating solution treated in Reference Examples 1 to 3 are presented in Table 1. As can be seen from Table 1, it has been found that the concentration of the carboxylic acid and the concentration of the alcohol in Reference Example 1 are lower than those in Reference Examples 2 and 3. In addition, it has been found that the concentration of the additive is decreased in Reference Example 2 but it is not decreased in Reference Example 1.

TABLE 1 Concentration Concentration Con- Con- Con- Con- Impurity removal of Concentration of centration of centration centration centration mechanism carboxylic acid of alcohol copper sulfate sulfuric acid of PEG of SPS of JGB Reference Ion chromatography  34 mg/L  56 mg/L 200 g/L 100 g/L 100 mg/L 8 mg/L 10 mg/L Example 1 apparatus and distillation apparatus Reference Activated carbon filter 103 mg/L  172 mg/L 200 g/L 100 g/L  18 mg/L 4 mg/L  5 mg/L Example 2 Reference Nil 719 mg/L 1198 mg/L 200 g/L 100 g/L 100 mg/L 8 mg/L 10 mg/L Example 3

(Function Confirmation of Plating Device)

Next, the effect of the plating device belonging to the technical scope of the present invention was investigated with reference to Examples and Comparative Examples. More specifically, a change of the plated film was confirmed through a continuous operation using the plating device. A copper sulfate plating solution was prepared so as to contain 200 g/L of copper sulfate pentahydrate, 100 g/L of sulfuric acid, and 50 mg/L of hydrochloric acid, and 100 mg/L of polyethylene glycol, 8 mg/L of bis(3-sulfopropyl) disulfide, and 10 mg/L of the Janus Green B as the additive.

Example 1

The plating solution prepared above was introduced into a plating device in which an ion chromatography apparatus as an impurity removal mechanism was connected to the plating tank, and the plating was conducted. The conditions for use of the ion chromatography apparatus were the same as the conditions when confirming the function of the impurity removal mechanism.

Example 2

The plating solution prepared above was introduced into a plating device in which a distillation apparatus as an impurity removal mechanism was connected to the plating tank, and the plating was conducted. The conditions for use of the distillation apparatus were the same as the conditions when confirming the function of the impurity removal mechanism.

Example 3

The plating solution prepared above was introduced into a plating device in which an ion chromatography apparatus (carboxylic acid removal mechanism) and a distillation apparatus (alcohol removal mechanism) were connected to the plating tank as illustrated in FIG. 1, and the plating was conducted. The conditions for use of the ion chromatography apparatus and the distillation apparatus were the same as the conditions when confirming the function of an impurity removal mechanism.

Example 4

The plating solution prepared above was introduced into a plating device in which an ion chromatography apparatus (carboxylic acid removal mechanism) and a distillation apparatus (alcohol removal mechanism) were connected to the management tank as illustrated in FIG. 2, and the plating was conducted. The conditions for use of the ion chromatography apparatus and the distillation apparatus were the same as the conditions when confirming the function of an impurity removal mechanism.

Comparative Example 1

As a comparative example, the plating solution prepared above was introduced into a plating device of the prior art illustrated in FIG. 4, and the plating was conducted.

In Examples 1 to 4 and Comparative Example 1, a substrate obtained by coating a resist on a Si wafer so as to have a thickness of 18 μm and patterning the resultant by a known photolithography technique was used. The above substrate was plated so as to have a plating thickness of 15 μm by an electroplating method using the devices of Example 1, Example 2, Example 3, Example 4, and Comparative Example 1. This was carried out by 10 sheets per one day, and the appearance of the plated film after one day, 30 days, 60 days, and 90 days was confirmed.

The results thereof are presented in Table 2. As can be seen from the results presented in Table 2, it is possible to obtain a plated film without fogging during a continuous operation for a long period of time in any of Examples as compared to Comparative Example 1. It is possible to obtain a plated film without fogging during a continuous operation for a long period of time in Example 1 when Example 1 is compared to Example 2. In addition, it is possible to obtain a plated film without fogging during a continuous operation for a long period of time in Example 4 when Example 3 is compared to Example 4.

TABLE 2 Place to which impurity Impurity removal removal mechanism is Number of substrate fogged mechanism connected After one day After 30 days After 60 days After 90 days Example 1 Ion chromatography Plating tank 0 sheet of 10 0 sheet of 300 3 sheets of 600 — apparatus sheets sheets sheets Example 2 Distillation apparatus Plating tank 0 sheet of 10 0 sheet of 300 5 sheets of 600 — sheets sheets sheets Example 3 Ion chromatography Plating tank 0 sheet of 10 0 sheet of 300 0 sheet of 600 5 sheets of apparatus and sheets sheets sheets 900 sheet distillation apparatus Example 4 Ion chromatography Management tank 0 sheet of 10 0 sheet of 300 0 sheet of 600 0 sheet of 900 apparatus and sheets sheets sheets sheets distillation apparatus Comparative Nil — 0 sheet of 10 9 sheets of 300 — — Example 1 sheets sheets 

What is claimed is:
 1. A plating device comprising: a plating tank; and an impurity removal mechanism connected to the plating tank so as to remove impurities from a plating solution in the plating tank or a plating solution supplied to the plating tank, wherein the impurity removal mechanism includes at least one of a carboxylic acid removal mechanism and an alcohol removal mechanism.
 2. The plating device according to claim 1, further comprising: a management tank for receiving the plating solution supplied from the plating tank and supplying the plating solution received to the plating tank again, wherein at least one of the carboxylic acid removal mechanism and the alcohol removal mechanism is connected to the management tank.
 3. The plating device according to claim 1, wherein the impurity removal mechanism includes both of a carboxylic acid removal mechanism and an alcohol removal mechanism.
 4. The plating device according to claim 2, wherein the impurity removal mechanism includes both of a carboxylic acid removal mechanism and an alcohol removal mechanism. 